01A lily pad doubles in size every day. It takes 48 days to cover the entire pond. How long did it take to cover half the pond?
Answer
47 days. On day 47 it covered half — then doubled on day 48 to cover it all.
Open the interactive card →Curated by JAKH
16 Logic Puzzles With Answers and Explanations
Work through 16 logic puzzles that reward careful reading, deduction, and a little arithmetic. Each answer includes the key reasoning.
02A girl has as many brothers as sisters. Each brother has half as many brothers as sisters. How many children are there in total?
Answer
7 children: 4 girls and 3 boys. Each girl has 3 brothers and 3 sisters. Each boy has 2 brothers and 4 sisters.
Open the interactive card →03You overtake the person in 2nd place in a race. What place are you in now?
Answer
2nd place. You took their position — you did not overtake 1st place.
Open the interactive card →04Lina, Sami, and Noor each chose a different drink: tea, coffee, or juice. Sami chose coffee, Noor did not choose juice, and Lina did not choose tea. Who chose each drink?
Answer
Noor chose tea, Sami chose coffee, and Lina chose juice. Once coffee is assigned to Sami, Noor's only allowed drink is tea, leaving juice for Lina.
Open the interactive card →05Three books—red, green, and blue—stand in a row. The red book is to the left of the green book, and the blue book is to the right of the green book. What is their order from left to right?
06When I was 6 my sister was half my age. Now I am 70. How old is my sister?
Answer
67. She was 3 when I was 6 — so she is always 3 years younger than me.
Open the interactive card →07A two-digit number has digits that add to 11. Reversing its digits makes the number 27 greater. What is the original number?
Answer
47. If the tens digit is a and the ones digit is b, then a+b=11 and 9(b−a)=27, so b−a=3. Thus a=4 and b=7.
Open the interactive card →08Is 8% of 50 the same as 50% of 8?
09What is the sum of all integers from 1 to 100?
10A treasure is in exactly one of three boxes. Box 1 says, “The treasure is in Box 2.” Box 2 says, “The treasure is not in Box 2.” Box 3 says, “The treasure is not in Box 1.” Exactly one note is true. Which box holds the treasure?
Answer
Box 1. If the treasure is there, only Box 2's note is true. Putting it in Box 2 or Box 3 makes two notes true.
Open the interactive card →11On a 24-hour digital clock, 12:21 is palindromic. What is the next palindromic time, and how many minutes later is it?
12A cube is painted on all six faces and cut into 27 equal smaller cubes. How many small cubes have exactly two painted faces?
Answer
12. Each of the cube's 12 edges has one non-corner small cube, and each such cube has exactly two painted faces.
Open the interactive card →13In a class of 30 students, 18 study Arabic, 14 study English, and 5 study neither language. How many study both Arabic and English?
Answer
7. Twenty-five students study at least one language, so the overlap is 18 + 14 − 25 = 7.
Open the interactive card →14A three-digit vault code has distinct digits. The first digit is twice the third, the middle digit is one greater than the third, and all three digits add to 13. What is the code?
Answer
643. Let the third digit be t. The digits are 2t, t+1, and t, so 4t+1=13 and t=3.
Open the interactive card →15A snail is at the bottom of a 10-metre well. Each day it climbs 3 metres and each night slips back 2 metres. How many days does it take to escape?
Answer
8 days. After 7 days the snail is at 7 m. On day 8 it climbs 3 m to reach 10 m and escapes before slipping back.
Open the interactive card →16What is the last digit of 7¹⁰⁰?
Answer
1. The last digits of powers of 7 cycle in groups of 4: 7, 9, 3, 1. Since 100 ÷ 4 = 25 exactly, the last digit is 1.
Open the interactive card →